My dog (large black lab) very rarely gets left alone but when he does I give him a raw marrow bone. I was advised to do this by a vet who said that the big cooked ones can splinter and injure them and that anything smaller they can choke on. DDog has hurt a tooth and I took him to the vet (different one this time) who was very disapproving of the raw bone thing and said that it could be responsible for his tooth injury.
So, going forward what can I use that will keep him entertained for an hour or so, that isn't going to make him put on loads of weight and isn't going to cause tooth / choking problems.